THE TYMPANUM. 



637 



Fig. 449. 



Btapes, enclose fi small triangular or arched space, which in the recent 

 state is occupied by a thin membrane stretched across, _ A shallow 

 groove runs round the opposed surfaces of the bone, and into this the 

 membrane is received. 



LIGAMENTS AND MUSCLES OF THE TYMPANUM. 



Ligaments.— In the articulations of the small bones of the ear with 

 one another the connection is strengthened by ligamentous fibres.* 



Their attachment to the walls of the tympanum is effected partly by 

 the reflections of the mucous membrane lining that cavity, but chiefly 

 by muscles and by the following ligaments. 



The anterior ligament of 

 the malleus is a compara- 

 tively strong and broad band 

 of, for the most part, short 

 fibres, which connects the an- 

 terior wall of the tympanum 

 close to the Glaserian fissure 

 with the base of the processus 

 gracilis and the anterior part 

 of the body of the malleus. 



The suspensory ligament of 

 the malleus consists of a small 

 bundle of fibres, which passes 

 downwards and outwards 

 from the roof of the tympa- 

 num to the head of the 

 malleus, and serves to check 

 its movement in an outward 

 direction. 



The posterior ligament of 

 the incus extends from near 

 the point of the short cms 

 directly backwards towards 

 the posterior wall of the tym- 

 panum, where it is attached 

 near to the entrance to the 

 mastoid cells. 



Arnold describes an upper liga- 

 ment which attaches the incus, 

 near its ra-ticulation with the 

 malleus, to the roof of the tym- 

 panum. 



Muscles. — There are 

 three well-determined mus- 

 cles of the tympanum. Scim- 

 merring describes four, and 

 some authors a larger number ; but the descriptions of these last mus- 

 cles are not confirmed by later research. Of the three muscles generally 

 recognised, two are attached to the malleus, and one to the stapes. 



* These articulations are commonly described as s^.ijovial joints, but, according to 

 Erunner (Knapp and l\roos' Archiv, 1874), they are more of the nature of symphyses, 

 with fibrocartilage between the contiguous surfaces. 



Fig. 449. — View of the Cavity op the Right 

 Tympanum from above. 

 The cavity of the tympanum and a part of the 

 labyi-inth have been exposed by a horizontal section 

 removing the upper part of the temporal bone. 1, 

 posterior semicircular canal opened ; 2, the cavity 

 of the cochlea opened ; 3, osseous part of the 

 Eustachian tube ; 4, head of the malleus ; 5, 

 incus ; 6, stapes, witli its base set in the fenestra 

 ovalis ; 7, tensor tympani muscle ; 8, stapedius. 



